This invention pertains to aldol condensations catalyzed by heat-treated synthetic anionic clay minerals and more particularly to the use of these catalysts for the conversion of acetone to mesityl oxide and isophorone.
The aldol condensation of active hydrogen-containing organic carbonyl compounds has found wide use in the chemical industry for the synthesis of a myriad of organic compounds. The earliest catalysts used for this condensation reaction were bases, such as, alkali metal hydroxides which have been used for the production of 2-ethylhexanediol-1, 3, 2-ethylhexanol-1, diacetone alcohol, isophorone, mesityl oxide, methylisoamyl ketone, methylisobutyl ketone and the like.
A variety of methods has been disclosed in the literature for converting, for example, acetone by aldol condensation into a wide spectrum of products particularly isophorone and mesityl oxide which are used in industrial solvents and as chemical intermediates for resins, dyes, intersecticides, and the like. By-products which arise from the general aldol condensation reaction with acetone include diacetone alcohol, 4,4-dimethyl-hepta-2,6-dione, 4,6-dimethyl-hepta-3,5-diene-2-one, 3,5,5-trimethyl cyclohex-3-ene-one, mesitylene, 2,2,6,6-tetramethyl tetrahydropyran-4-one, xylitones, and isoxylitones, as well as various unidentified high boilers and tars. The specificity of the reaction must be controlled for commercial success in order to direct conversion of acetone to the desired end products.
Examples of prior catalysts used for conversion acetone to isophorone and mesityl oxide are: alkali metal hydroxides, such as, sodium, potassium, and lithium hydroxide, alkaline earth hydroxides, such as calcium, magnesium, strontium and barium hydroxide; calcium aluminate, calcium borate, potassium zincate, magnesium plumbate, barium aluminate, lithium plumbate, sodium borate, strontium stannate, potassium stannate, calcium borate, magnesium antimonate, sodium antimonate, calcium arsenate, sodium arsenate, potassium titanate, calcium zincate, magnesium aluminate, beryllium aluminate, cesium borate, rubidium arsonate, lithium phosphate, magnesium oxide, and the like.
In addition a recently discovered magnesium-aluminum hydroxide based catalyst has been described in U.S. Pat. No. 4,165,339 which affords efficiencies of about 80 percent (acetone to mesityl oxide and isophorone) at a conversion of about 15 to 18 percent per pass.
It is an object of this invention to provide an aldol condensation catalyst particularly for the conversion of acetone to mesityl oxide and isophorone having both enhanced efficiencies and conversions of acetone.
It is a further object of this invention to control the condensation of acetone to produce chiefly mesityl oxide and isophorone and in addition to limit the molar ratio of mesityl oxide: isophorone produced to a low value, preferably less than one, to conform to the commercial demand for these two products.
It is still a further object of this invention to provide a catalyst for this aldol condensation of acetone having the following properties:
High and constant activity PA0 Reproducible activity PA0 Long catalyst life PA0 Ability to be regenerated readily PA0 Consistent in selective production of mainly mesityl oxide and isophorone PA0 Cheaper and available PA0 The general method for the preparation of the catalyst is illustrated by the preparation of Mg/Al/carbonate hydrotalcite which involves the addition of mixed magnesium/aluminum nitrates, sulphates or chlorides as an aqueous solution to a solution of a stoichiometric amount of sodium hydroxide and carbonate at about 25.degree.-35.degree. C. with vigorous stirring over about a several-hour period producing a slurry. This slurry is then heated for about 18 hours at about 50.degree.-200.degree. C. (preferably 60.degree.-75.degree. C.) in order to allow a limited amount of crystallization to take place. After filtering the solids, and thorough washing and drying, the dry solids are recovered. PA0 This procedure is readily adaptable to variations in the Mg/Al ratio, the anions, and cation substitution. The presence of the sodium carbonate materially enhances the rate of filtration; the absence of sodium carbonate results in a mud which is very difficult to filter. PA0 A=Total Acetone equivalents fed PA0 B=Total Acetone equivalents in product(s) PA0 MSO=Total equivalents of acetone in the mesityl oxide product PA0 I=Total equivalents of acetone in isophorone product.
It is also an object of this invention to provide a catalyst and method for the aldol condensation of active hydrogen-containing organic carbonyl compounds in general.